Container inspection system and method

ABSTRACT

An apparatus for inspecting a container to determine whether such container has properties different from a particular standard by utilizing a long life radioactive isotope source that emits low energy gamma radiation. The invention also relates to a method of making a very compact but safe housing to encapsulate the low energy gamma radiation source used in the apparatus. The housing utilized to encapsulate the radioactive source can provide adequate shielding to protect nearby personnel by using a metal such as stainless steel because of the low energy output of the source. A thin window, formed as an integral part of the housing, freely passes a portion of the source radiation that is used for inspection purposes. The housing is constructed from standard metal bar stock in a particular manner that minimizes the possibility that the thin window will include defects or impurities contained within the metal bar stock. A collimation means is utilized in front of the source housing window to confine the beam of radiation that emanates from the source through the window. This collimated radiation beam is directed at the area of the container to be examined and the amount of radiation passing through the container provides an indication as to whether or not the container has properties different from a particular standard.

United States Patent [191 Calhoun [451 Jan. 8, 1974 CONTAINER INSPECTIONSYSTEM AND METHOD [75] Inventor: Fredrick L. Calhoun, Torrance,

Calif.

[73] Assignee: Industrial Dynamics Company, Ltd.,

Torrance, Calif.

[22] Filed: Mar. 5, 1971 [21] Appl. No.: 121,321

52 05. Cl. 250/106 s [51] Int. Cl. G21f 5/02 [58] Field of Search250/43.5 D, 83.3 D, 250/106 S, 108 R [56] References Cited UNITED STATESPATENTS 3,001,076 9/1961 Crump 250/83.3 D X 3,126,484 3/1964 Meeder eta1... 250/108 R X 3,050,626 8/1962 Dukes et a1 250/83.3 D 3,064,35711/1962 Butters 250/83.3 D X 3,132,247 5/1964 Wright 250/83.3 D3,100,841 8/1963 Reider 250/83.3 D X 3,683,186 8/1972 Tompkins 250/105Primary ExaminerJames W. Lawrence Assistant Examiner-Davis L. WillisAttorney-Smyth, Roston & Pavitt 571 ABSTRACT An apparatus for inspectinga container to determine whether such container has properties differentfrom a particular standard by utilizing a long life radioactive isotopesource that emits low energy gamma radiation. The invention also relatesto a method of making a very compact but safe housing to encapsulate thelow energy gamma radiation source used in the apparatus.

The housing utilized to encapsulate the radioactive source can provideadequate shielding to protect nearby personnel by using a metal such asstainless steel because of the low energy output of the source. A thinwindow, formed as an integral part of the housing, freely passes aportion of the source radiation that is used for inspection purposes.The housing is constructed from standard metal bar stock in a particularmanner that minimizes the possibility that the thin window will includedefects or impurities contained within the metal bar stock.

A collimation means is utilized in front of the source housing window toconfine the beam of radiation that emanates from the source through thewindow. This collimated radiation beam is directed at the area of thecontainer to be examined and the amount of radiation passing through thecontainer provides an indication as to whether or not the container hasproperties different from a particular standard.

11 Claims, 6 Drawing Figures I CONTAINER INSPECTION SYSTEM AND METHODThis invention relates to apparatus for inspecting a container todetermine whether such container has properties different from aparticular standard. The invention also relates to methods of producinga compact sealed housing for a low energy gamma emitting radioisotopesource and of assembling the housing and the source.

Radiation from radioisotopes and other sources has been used in theprior art to determine whether a container has properties different froma particular standard. For example, radiation has been passed through acontainer to determine whether liquid has been filled in the containerto a desired height. If the liquid is filled to the desired height,radiation passing through the container at the desired height will beabsorbed by the liquid. If the container has not been filled with liquidto the desired height, the radiation will pass through the container. Inthis way, the amount of radiation passing through the container willprovide an indication as to whether or not the liquid in the containerhas been filled to the desired height.

The radioisotope sources previously in use to detect the characteristicsof the container have had certain disadvantages primarily resulting fromtheir properties of providing gamma radiation at high energy levels.Some typical examples of previously used radioisotopes are Cesium-137with a gamma energy output of 661.6

7 KEY (thousand electron volts) and Cobalt-60 with a gamma energy outputof 1331.6 KEV. One digd vantage has been that the source has had to bepacked in heavy, bulky shielding units in order to be certain that theradiation from the source will not harm people standing close to thesource. Another diadvantage has been that the detection of the radiationpassing through the containers has not been very efficient since theradiation detectors are inherently less sensitive to high energy gammaradiation.

This invention provides a sealed radioisotope source which overcomes theabove disadvantages by providing gamma radiation at a low energy level.By providing a source whose radiation is at a low energy level, theshielding for the source can be relatively small and compact.Furthermore, the radiation passing through the container can be moreefficiently detected.

Although the low energy gamma radiation is easy to shield so that strayradiation will not harm personnel working in close proximity, adifficulty is encountered in providing a properly sealed housing thatdoes not absorb all of the radiation from the source since some isrequired for inspection purposes. Safety requirements usually dictatethe use of double fusion welds to seal all radioisotopes that areharmful to human beings. A housing must be designed so that double sealscan be made and also provide a very thin section or window so the lowenergy radiation can pass through relatively unimpeded.

Due to the use of low energy gamma radiation, adequate shielding can beobtained from a metal such as stainless steel instead of heavier metalssuch as lead re quired by the high energy sources. The use of stainlesssteel or a similar metal allows the source housing to be formed so thatthe thin window is an integral part of the housing. This procedurecannot be used with the high energy isotopes. Since the window is verythin, in the order of only 0.006 inch, great care must be taken toinsure the mechanical integrity and also to minimize the possibility ofthe window containing any impurities or defects that may be in the metalstock from which it is made. These imperfections in the window couldcause leakage to the radioactive material and thus endanger persons inthe vicinity of the housing.

The housing is made from standard rolled or elongated metal bar stockand is positioned in the bar stock so as to minimize the possibility ofthe window containing any impurities or defects contained in the stock.The majority of impurities in any rolled bar stock are contained in asection in the middle portion of the stock and are usually elongated inthe direction of rolling. The housing is positioned in the bar stock sothe thin window portion is near the edge of the stock and the plane ofthe window is parallel to the direction that the stock has been rolled.This procedure assures that the window will be placed in the portion ofthe bar stock where the minimum number of impurities and defects arelocated and, if such are present, they will lie in the plane of thewindow and not perpendicular to it. Due to the geometry described above,it is desirable, from a practical viewpoint, to make two housings fromeach section of bar stock. This procedure allows the full bar to beutilized.

The radioactive source material is disposed in a cavity in the housingin front of the thin window and a first shield is placed behind thesource and sealed to the housing by some means such as fusion welding. Asecond shield is placed behind the first shield and is also sealed tosaid housing. This completes the basic housing and source assembly. Foroperational safety and maintenance purposes, a bar having a collimatingaperture is slidable in another slot type cavity in front of the window.In one position of the bar, the aperture is aligned with the thin windowso that radiation from the source is able to pass through the window andthe aperture to the container being tested. When the bar is in positionfor radiation to pass through the aperture to the container, the amountof radiation passing through the container provides an indication as tothe properties of the container such as the height of fill of liquid inthe container. In other positions of the slidable bar, the aperture ismisaligned with the thin window so that radiation from the source isunable to pass through the bar to the container.

In the drawings:

FIG. 1 is a schematic elevational view of apparatus for inspecting acontainer for certain properties such as the height of fill of liquid inthe cotainer;

FIG. 2 is a perspective view of bar stock from which a housing includedin the embodiment shown in FIG. 1 is formed;

FIG. 3 is a plan view of the end of the bar stock schematicallyillustrating the formation of a pair of housings from the bar stockshown in FIG. 2, the housing being shown in partially completed form;

FIG. 4 is a sectional view illustrating the construction of the housingin completed form and further illustrat ing the disposition in thehousing of other members including a source of radiation;

FIG. 5 is a perspective view of the source of radiation shown in FIG. 4;and

FIG. 6 is a perspective view of the apparatus including the housing forproviding a controlled passage of radiation to a container.

In the embodiment shown in FIG. 1, a container is adapted to be testedfor particular characteristics. For example, the container may be testedto determine whether it is filled with liquid 12 such as a beverage toat least a particular height. If the container is not filled at least tothe particular height, a dissatisfied customer may result.

The height of the liquid in the container is determined by the apparatusschematically shown in FIG. 1 as the container is advanced by a conveyor14 in a direction into the plane of the paper. As the container 10 isadvanced by the conveyor 14, it moves past a testing station whichincludes a source 16 of radiation. The source 16 may be disposed in ahousing schematically illustrated as 18 which shields the source 16 sothat radiation cannot pass into the atmosphere in the area surroundingthe source. As will be appreciated, such passage of radiation isundesirable since it may injure a person in the vicinity of the source16. The housing 18 is provided with an aperture 20 through whichradiation from the source is directed.

The source 16 may preferably constitute Americium- 241. Americium-24l isadvantageous since it provides gamma rays at low energy. The primarygamma output is approximately 60 KEV. Because of the low energy of 25the radiation, the housing 18 shielding the source 16 can be small,relatively thin-walled and compact. The low energy radiation travelsthrough the container 10 and the liquid in the container to a detector22 such as a scintillation counter at the opposite side of the containerfrom the source 16.

The aperture 20 is disposed so that radiation from the source 16 passesthrough the container 10 at approximately the level which is desired forthe liquid in the container. When the liquid in the container 10 is ator above the desired level, the liquid tends to absorb a substantialportion of the radiation from the source 16 so that only a relativelysmall amount of radiation passes to the detector 22. However, when theliquid in the container 10 is below the desired level, the radiationpasses through the container without much absorption. Accordingly, thesignal produced by the detector 22 is dependent upon the level of theliquid in the container.

The signal from the detector 22 is introduced to processing circuitry24. The processing circuitry compares the amplitude of the signal fromthe detector 22 with a signal having a particular amplitudecorresponding to the amplitude of the signal produced by the detector 22when the liquid in the container is at or above the desired level. Whenthe amplitude of the signal from the detector 22 is above the particularamplitude, the processing circuitry 24 introduces a signal to rejectioncircuitry 26 to obtain a rejection of the container. This rejection isdelayed for a short period of time so that the container can move pastthe inspection station. When the container is rejected, it is divertedfrom the conveyor 14 to a rejection station.

It will be appreciated that the apparatus shown in FIG. 1 and describedabove for determining the height of fill of liquid in a container isonly by way of illustration and that the same apparatus can be used fora number of other tests. For example, the system including the radiationsource 16 and the detector 22 can be used to detect cartons to determinethat the cartons are fully stacked with the containers in a number ofdifferent rows and columns in the cartons. If a container is missingfrom a carton, the rejection circuitry 26 is operated to divert thecarton to the rejection station.

The housing 18 may be constructed in a manner similar to thatillustrated in FIG. 4. The housing 18 may be made from a suitable metalsuch as a Type 304 stainless steel having a low carbon content. A metalsuch as stainless steel may be used since it absorbs the radiation fromthe source 16 because of the low energy gamma rays from the source.Preferably, the stainless steel is vacuum melted when it is formed sincevacuum melting eliminates the majority of impurities such as inclusionsand stringers during the melting process. Impurities such as inclusionsand stringers are undesirable since they provide weak spots where breaksmay occur in the thin metal window such that radioactive material fromthe source may be able to permeate through such breaks and endanger thelives of persons in the vicinity of the source. The impurities aremainly composed of oxides, sulfides, silicates and corundum.

When the stainless steel for the housing 18 is vacuum melted to form barstock such as illustrated at 30 in FIG. 2, the stringers and inclusionsare located in the highest density at the center of the bar stock. Thesestringers and inclusions tend to extend in a direction parallel to thedirection of rolling of the bar stock so that the inclusions andstringers would tend to extend from the left to right in FIG. 2. As willbe described in detail subsequently,'the housing 18 is formed in amanner to minimize the existence of any impurities such as inclusionsand stringers in the housing.

As previously stated, it is desirable to make a pair of housings fromeach section of bar stock so that the entire cross section of the stockcan be utilized. Pairs of housings 18 are formed so that ends 32 of thehousings constitute ends 34 of the bar stock. This places the windowareas near the edge of the bar stock where the minimum number of defectsand inclusions are located. The area of high concentration of defectsand inclusions 38 is near the ends 36 of the housings. This is not acritical area of the housings and most of the metal in this area ismachined away to form the cavity in which the source is placed.

The cavity 40 is provided with a beveled edge 42 at its outer end, thebeveled edge having a relatively great diameter. The cavity 40 alsoincludes a straight-walled portion 44 extending inwardly from thebeveled edge 42 and having a relatively great diameter. A cavity portion46 having a reduced diameter extends inwardly from the cavity portion 44and a cavity portion 48 having an even further reduced diameter extendsinwardly from the cavity portion 46.

A slot cavity generally indicated at 50 is provided in the end 32 of thehousing. The slot cavity 50 is provided with a portion 52 of anintermediate width and with a portion 54 of increased width. A cavityportion 56 of relatively small width extends inwardly from the cavityportion 54 to define a thin window 58 with the cavity portion 48. Thewindow 58 has a thickness in the order of 0.006 inch. This thickness isnot sufficient to prevent radiation from the source 16 from passingthrough the window. Since the window 58 is relatively thin, anystringers or other imperfections in the window could possibly becomeloosened during machining of the window since they are vulnerable to anymechanical stress or corrosion.

The source 16 may be formed from Americium-24l mixed with a suitablematerial such as ceramic enamel.

For example, the ceramic enamel may contain approximately 100millicuries of Americium-24l. The enamel is fired at a suitabletemperature such as approximately l,l C. in a slit 64 in a retainershield 66 (FIG. which is made from a suitable material such as Type 304stainless steel. By disposing the Americium-24l in the ceramic enameland firing it into the retainer shield 66, any tendency for theAmericium-24l to migrate outside of the housing is minimized even of thewindow 58 should be accidentally punctured.

The retainer shield 66 is shaped so that it fits snugly in the cavityportions 48 and 46 in the housing, with the source 16 being disposedadajcent the window 58. The retainer shield 66 is suitably sealed to thehousing as at 62. A second shield 68 made from a suitable material suchas Type 304 stainless steel is in turn disposed in the cavity portion 44to cover the retainer shield 66 and is suitably sealed to the housing asat 69. The method described above provides a double seal thus minimizingthe possibility of any radioactive material leaking from the sourcehousing.

A sliding shield or bar 70 made from a suitable material such as a Type304 stainless steel is disposed in the cavity slot 50 of the housing 18and is provided with flange portions 72 for disposition in the cavityportion 54. The sliding shield 70 is slidable in the cavity slot 50 andis provided with a collimating aperture 74 (FIG. 4) which extendsthrough the sliding shield 70 for alignment with the window 58 in oneposition of the shield.

When the collimating aperture 74 is aligned with the window 58,radiation from the source 16 is able to pass through the window and theaperture to the container to provide an indication of the properties ofthe container. However, when the sliding shield 70 is moved to aposition in which the collimating aperture 74 is misaligned with thewindow 58, the sliding shield 70 blocks the passage of radiation to thecontainer 10. The sliding shield 70 is used as a safety device toeffectively block the radiation from the source when maintenance isrequired in the unit. The sliding shield 70 is usually placed in theclosed position when the equipment is not operating. The sliding shield70 could be replaced by a shieldand collimating aperture that is anintegral part of the source housing if desired, but the sliding shieldand aperture offers more versatility to the unit.

In this way, the housing 18 is provided with the window 58 in a mannersuch that no impurities such as inclusions or stringers are provided inthe window. By preventing the disposition of any impurities in thewindow, breaks or holes cannot occur in the windows to allow theradioactive material to permeate through the breaks and holes andendanger the health and safety of persons in the immediate vicinity ofthe housing. The window is disposed adjacent the source 16 so thatradiation from the source is able to pass through the window and theaperture 74 in the shield when the shield is properly disposed relativeto the window.

Although this application has been disclosed and illustrated withreference to particular applications, the principles involved aresusceptible of numerous other application which will be apparent topersons skilled in the art. The invention is, therefore, to be limitedonly as indicated by the scope of the appended claims.

I claim:

I. An improved relatively compact, sealed radioisotope source of lowenergy gamma for use in nuclear gauging apparatus wherein variousmaterials are inspected, comprising a housing of a metal tending to haveimpurities present as a result of the processing of such metal,

said housing including means defining a first and second formed cavityat opposite ends thereof.

one of said cavities including a bottom wall and being in a portion ofsaid housing substantially free of impurities,

the other of said cavity being so positioned that the bottom wallthereof is located in a portion of the housing tending to besubstantially free of impurities while the cavity is formed in thatportion of the housing tending to be the area of relatively highconcentration of impurities,

said cavities being spaced from each other such that the spacedrespective bottom walls form a thin low energy gamma transmitting windowwhich is integral with said housing,

a source of radioactive material so sealed in said first cavity adjacentto said window as to provide low energy gamma radiation which passesthrough said window,

said window being substantially free of metallic impurities tending tocause leakage of said source material from said first cavity, and

movable means in said second cavity for alignment with said window inone position for collimating the emanating radiation and for blockingthe passage of radiation in a second position thereof.

2. In an apparatus as set forth in claim 1 further including shieldmeans in said first cavity at a position external to the source materialand sealed to the housing to prevent leakage of source material from thehousing through the first cavity and blocking all radiation through thefirst cavity so that emanating radiation passes only through saidintegral window.

3. In an apparatus as set forth in claim 1 wherein said movable meansincludes a'bar movably disposed in said second cavity and including acollimating aperture for alignment with the window, in one slidableposition of the bar, to provide for passage of gamma rays from thesource through the window and aperture.

4. In an apparatus as set forth in claim 1 wherein said source materialis an Americium-24l radioisotope.

5. ln an apparatus as set forth in claim 1 wherein said housing is oflow carbon vacuum melted stainless steel.

6. In an apparatus as set forth in claim 5 wherein said steel is a Type304 stainless steel.

7. In an apparatus as set forth in claim 1 wherein said window has athickness of less than 0.01 inches.

8. In an apparatus as set forth in claim 7 wherein said window has athickness of 0.006 inch.

9. In an apparatus as set forth in claim 2 wherein said shield meansincludes a first shield adjacent to the source and sealed to the housingand a second shield overlying said first shield and sealed to saidhousing.

10. In an apparatus as set forth in claim 1 wherein said housing is madefrom rolled bar stock,

said second cavity and said window being located in that portion of saidbar stock containing the minimum, if any-, rnetallic impurities.

l 1. An improved compact radioactive source for use in nuclear gaugingwherein the emitted radiation is low energy gamma, comprising a metalhousing having a portion thereof of reduced metal impurities anddefects, and a portion tending to include a relatively highconcentration of metal impurities and defects,

means forming a first cavity including a bottom wall in that portion ofthe housing of reduced metal impurities,

a second cavity so positioned as to be opposite said first cavity andoriented such that the bottom wall thereof is spaced from the bottomwall of the first cavity,

the bottom wall of said second cavity being in a portion of said housingsubstantially free of impurities and said second cavity being located ina portion of said housing tending to have a relatively highconcentration of metal impurities,

said cavities being spaced from each other such that the spaced bottomwalls thereof define a relatively thin window integral with said housingand being that portion of said housing separating said first and saidsecond cavities,

a source of radioactive material received in said second cavity andpositioned adjacent to said window,

means sealing said radioactive material in said second cavity wherebygamma radiation emanating therefrom passes through said window, and

collimating means positioned in said first cavity and movable to aposition in alignment with said window for collimating said emanatinggamma radiation and being movable to another position obstructingemanation of gamma radiation from said housing.

1. An improved relatively compact, sealed radioisotope source of lowenergy gamma for use in nuclear gauging apparatus wherein variousmaterials are inspected, comprising a housing of a metal tending to haveimpurities present as a result of the processing of such metal, saidhousing including means defining a first and second formed cavity atopposite ends thereof, one of said cavities including a bottom wall andbeing in a portion of said housing substantially free of impurities, theother of said cavity being so positioned that the bottOm wall thereof islocated in a portion of the housing tending to be substantially free ofimpurities while the cavity is formed in that portion of the housingtending to be the area of relatively high concentration of impurities,said cavities being spaced from each other such that the spacedrespective bottom walls form a thin low energy gamma transmitting windowwhich is integral with said housing, a source of radioactive material sosealed in said first cavity adjacent to said window as to provide lowenergy gamma radiation which passes through said window, said windowbeing substantially free of metallic impurities tending to cause leakageof said source material from said first cavity, and movable means insaid second cavity for alignment with said window in one position forcollimating the emanating radiation and for blocking the passage ofradiation in a second position thereof.
 2. In an apparatus as set forthin claim 1 further including shield means in said first cavity at aposition external to the source material and sealed to the housing toprevent leakage of source material from the housing through the firstcavity and blocking all radiation through the first cavity so thatemanating radiation passes only through said integral window.
 3. In anapparatus as set forth in claim 1 wherein said movable means includes abar movably disposed in said second cavity and including a collimatingaperture for alignment with the window, in one slidable position of thebar, to provide for passage of gamma rays from the source through thewindow and aperture.
 4. In an apparatus as set forth in claim 1 whereinsaid source material is an Americium-241 radioisotope.
 5. In anapparatus as set forth in claim 1 wherein said housing is of low carbonvacuum melted stainless steel.
 6. In an apparatus as set forth in claim5 wherein said steel is a Type 304 stainless steel.
 7. In an apparatusas set forth in claim 1 wherein said window has a thickness of less than0.01 inches.
 8. In an apparatus as set forth in claim 7 wherein saidwindow has a thickness of 0.006 inch.
 9. In an apparatus as set forth inclaim 2 wherein said shield means includes a first shield adjacent tothe source and sealed to the housing and a second shield overlying saidfirst shield and sealed to said housing.
 10. In an apparatus as setforth in claim 1 wherein said housing is made from rolled bar stock,said second cavity and said window being located in that portion of saidbar stock containing the minimum, if any, metallic impurities.
 11. Animproved compact radioactive source for use in nuclear gauging whereinthe emitted radiation is low energy gamma, comprising a metal housinghaving a portion thereof of reduced metal impurities and defects, and aportion tending to include a relatively high concentration of metalimpurities and defects, means forming a first cavity including a bottomwall in that portion of the housing of reduced metal impurities, asecond cavity so positioned as to be opposite said first cavity andoriented such that the bottom wall thereof is spaced from the bottomwall of the first cavity, the bottom wall of said second cavity being ina portion of said housing substantially free of impurities and saidsecond cavity being located in a portion of said housing tending to havea relatively high concentration of metal impurities, said cavities beingspaced from each other such that the spaced bottom walls thereof definea relatively thin window integral with said housing and being thatportion of said housing separating said first and said second cavities,a source of radioactive material received in said second cavity andpositioned adjacent to said window, means sealing said radioactivematerial in said second cavity whereby gamma radiation emanatingtherefrom passes through said window, and collimating means positionedin sAid first cavity and movable to a position in alignment with saidwindow for collimating said emanating gamma radiation and being movableto another position obstructing emanation of gamma radiation from saidhousing.